Guest
Should the used pins be left unconnected or should they be taken to ground?
V
Vidar Lřkken
Guest
elehman1@columbus.rr.com wrote:
--
MVH,
Vidar
www.bitsex.net
I suggest leaving _used_ pins alone...
--
MVH,
Vidar
www.bitsex.net
Guest
Sorry for my typing skills. I ment to say:
What do you do with unused pins?
<elehman1@columbus.rr.com> wrote in message
news:STR1e.21517$rL3.11988@fe2.columbus.rr.com...
What do you do with unused pins?
<elehman1@columbus.rr.com> wrote in message
news:STR1e.21517$rL3.11988@fe2.columbus.rr.com...
J
Jim Thompson
Guest
On Mon, 28 Mar 2005 16:54:01 -0800, Luhan Monat <x@y.z> wrote:
floating objects... on others they may be used as test points during
manufacture and are designated NC (no connection).
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
Try reading the data sheet? On some I/C's spare pins are just
floating objects... on others they may be used as test points during
manufacture and are designated NC (no connection).
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice
480)460-2350 | || E-mail Address at Website Fax
480)460-2142 | Brass Rat || http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
L
Luhan Monat
Guest
elehman1@columbus.rr.com wrote:
--
Luhan Monat (luhanis 'at' yahoo 'dot' com)
"The future is not what it used to be..."
http://members.cox.net/berniekm
Sell them on Ebay?
--
Luhan Monat (luhanis 'at' yahoo 'dot' com)
"The future is not what it used to be..."
http://members.cox.net/berniekm
C
CJT
Guest
elehman1@columbus.rr.com wrote:
--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form che...@prodigy.net.
internally, then logic should prevail.
--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form che...@prodigy.net.
Guest
<elehman1@columbus.rr.com> wrote:
the chip used, and the circuit it's used in." In general, unused
outputs can be left alone, unused inputs should probably be tied high
or low, sometimes through a resistor, but you can't tell without a
detailed schematic and a datasheet and/or application note for the
specific IC used. I can probably think of a dozen examples of where
my "general" rules above are wrong, for instance...
And everyone who replied meant to say: "It's entirely dependent on
the chip used, and the circuit it's used in." In general, unused
outputs can be left alone, unused inputs should probably be tied high
or low, sometimes through a resistor, but you can't tell without a
detailed schematic and a datasheet and/or application note for the
specific IC used. I can probably think of a dozen examples of where
my "general" rules above are wrong, for instance...
R
Robert
Guest
"Jim Thompson" <thegreatone@example.com> wrote in message
news:8k6h41ti49nk5kej0eoegfpa6s4lt5ruji@4ax.com...
the positive supply through a 1K resistor.
OR gate inputs are to be connected to ground.
Why this is recommended is obvious from the logic function the gates
perform.
If the unused inputs are not logic gate inputs it gets more complicated, as
Jim and others have mentioned.
Robert
news:8k6h41ti49nk5kej0eoegfpa6s4lt5ruji@4ax.com...
The recommendation for logic gates is to connect unused AND gate inputs to
the positive supply through a 1K resistor.
OR gate inputs are to be connected to ground.
Why this is recommended is obvious from the logic function the gates
perform.
If the unused inputs are not logic gate inputs it gets more complicated, as
Jim and others have mentioned.
Robert
J
Jim Thompson
Guest
On Tue, 29 Mar 2005 13:42:40 -0500 (EST), "Aidan Grey"
<apgrey@nospam.con> wrote:
easily forcing a test signal when trying to track a fault.
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
<apgrey@nospam.con> wrote:
I know digital designers who do this as standard practice... it allows
easily forcing a test signal when trying to track a fault.
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice
480)460-2350 | || E-mail Address at Website Fax
480)460-2142 | Brass Rat || http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
L
Larry Brasfield
Guest
"Aidan Grey" <apgrey@nospam.con> wrote in message
news:ncterlplorehfpn.ie4mn40.pminews@news.execulink.com...
It was only "necessary" for TTL, where the base-emitter
junction following a strapped-high input could be stressed
if forced into breakdown by excessive VCC. This is not
a concern with CMOS, where, by the time an input gate
is in jeapardy, so are many of the internal gates.
Another reason I've seen for strapping thru a resistor is
so, during board test development, canned routines can
be applied to the part, testing used and unused gates
alike. It takes a tiny extra effort to not test an unused
gate or ignore one that fails because its input cannot be
wiggled enough. (That practise always stuck in my craw,
since unit cost was among my responsiblities, but I heard
it from enough different test folks that I guess it could be
part of their lore of "good" practise.)
--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.
news:ncterlplorehfpn.ie4mn40.pminews@news.execulink.com...
It was only "necessary" for TTL, where the base-emitter
junction following a strapped-high input could be stressed
if forced into breakdown by excessive VCC. This is not
a concern with CMOS, where, by the time an input gate
is in jeapardy, so are many of the internal gates.
Another reason I've seen for strapping thru a resistor is
so, during board test development, canned routines can
be applied to the part, testing used and unused gates
alike. It takes a tiny extra effort to not test an unused
gate or ignore one that fails because its input cannot be
wiggled enough. (That practise always stuck in my craw,
since unit cost was among my responsiblities, but I heard
it from enough different test folks that I guess it could be
part of their lore of "good" practise.)
--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.
A
Aidan Grey
Guest
On Mon, 28 Mar 2005 23:09:00 GMT, elehman1@columbus.rr.com wrote:
open, it is possible the chip will start "oscillating", if the input is
moving
between on and off. This will probably not affect the chip, but may cause
odd problems elsewhere in the circuit.
At one time, it was the military practise to attach unused inputs through
a 1K resister to VCC. Doing this is longer thought necessary, just attach it
directly.
Aidan Grey
Unused inputs should be tied to either VCC or ground. If they are left
open, it is possible the chip will start "oscillating", if the input is
moving
between on and off. This will probably not affect the chip, but may cause
odd problems elsewhere in the circuit.
At one time, it was the military practise to attach unused inputs through
a 1K resister to VCC. Doing this is longer thought necessary, just attach it
directly.
Aidan Grey
P
Pooh Bear
Guest
Jim Thompson wrote:
resistor.
Be aware that *some* pins are called N/C by the manufacturer. Best to leave these
alone.
Graham
That's the first good example I've heard mentioned for including a series
resistor.
Be aware that *some* pins are called N/C by the manufacturer. Best to leave these
alone.
Graham
J
John Fields
Guest
On Tue, 29 Mar 2005 13:42:40 -0500 (EST), "Aidan Grey"
<apgrey@nospam.con> wrote:
That's true except for multiple-emitter TTL, in which case the
resistor should be added if the input is pulled high. It's all
spelled out here:
http://focus.ti.com/lit/an/sdya009c/sdya009c.pdf
There is, however, the curious note on the bottom of page 7...
--
John Fields
<apgrey@nospam.con> wrote:
---
That's true except for multiple-emitter TTL, in which case the
resistor should be added if the input is pulled high. It's all
spelled out here:
http://focus.ti.com/lit/an/sdya009c/sdya009c.pdf
There is, however, the curious note on the bottom of page 7...
--
John Fields
J
Jim Thompson
Guest
On Tue, 29 Mar 2005 20:39:28 +0100, Pooh Bear
<rabbitsfriendsandrelations@hotmail.com> wrote:
required resistors on unused inputs, but edicted, "No system shall
contain a one-shot." ;-)
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
<rabbitsfriendsandrelations@hotmail.com> wrote:
One very good designer I knew (he's now deceased) not only adamantly
required resistors on unused inputs, but edicted, "No system shall
contain a one-shot." ;-)
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice
480)460-2350 | || E-mail Address at Website Fax
480)460-2142 | Brass Rat || http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
R
Robert Monsen
Guest
Aidan Grey wrote:
to VCC through a 10k resistor. I'm not sure, but I believe they are are
afraid of SCR latchup, which can occur with CMOS inputs if there is more
than some small amount of current into the pin above Vcc. Perhaps they
have seen this happen during startup with a big cap near the power pin,
or with glitches on the power rail.
I bet JT will know if this is really possible, or just an application
engineer's fantasy. I think the newer pics don't have this in their
datasheet anymore.
--
Regards,
Robert Monsen
"Your Highness, I have no need of this hypothesis."
- Pierre Laplace (1749-1827), to Napoleon,
on why his works on celestial mechanics make no mention of God.
Some of the microchip datasheets say you should connect the MCLR input
to VCC through a 10k resistor. I'm not sure, but I believe they are are
afraid of SCR latchup, which can occur with CMOS inputs if there is more
than some small amount of current into the pin above Vcc. Perhaps they
have seen this happen during startup with a big cap near the power pin,
or with glitches on the power rail.
I bet JT will know if this is really possible, or just an application
engineer's fantasy. I think the newer pics don't have this in their
datasheet anymore.
--
Regards,
Robert Monsen
"Your Highness, I have no need of this hypothesis."
- Pierre Laplace (1749-1827), to Napoleon,
on why his works on celestial mechanics make no mention of God.
J
John Fields
Guest
On Tue, 29 Mar 2005 13:53:53 -0600, John Fields
<jfields@austininstruments.com> wrote:
John Fields
<jfields@austininstruments.com> wrote:
input
--
John Fields
J
Jim Thompson
Guest
On Tue, 29 Mar 2005 12:20:53 -0800, Robert Monsen
<rcsurname@comcast.net> wrote:
applications engineer's.
Since tying MCLR to VCC prevents a differential, I doubt that anything
untoward can happen.
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
<rcsurname@comcast.net> wrote:
Anything's possible, but this is an ESD engineer's fantasy, not an
applications engineer's.
Since tying MCLR to VCC prevents a differential, I doubt that anything
untoward can happen.
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice
480)460-2350 | || E-mail Address at Website Fax
480)460-2142 | Brass Rat || http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
R
repatch
Guest
On Tue, 29 Mar 2005 13:42:40 -0500, Aidan Grey wrote:
zeros the tris bit for port a, when he/she meant port b... let's just say
leaving it floating is a FAR better result...
The resistor is still necessary IMHO, if only to save a person from their
own mistakes.
Right, and everything will be fine, until a new program is uploaded that
zeros the tris bit for port a, when he/she meant port b... let's just say
leaving it floating is a FAR better result...
The resistor is still necessary IMHO, if only to save a person from their
own mistakes.
R
repatch
Guest
On Tue, 29 Mar 2005 13:33:15 -0700, Jim Thompson wrote:
Except of course when you try and in-circuit program the PIC...
J
John Fields
Guest
On Tue, 29 Mar 2005 16:17:31 -0500, repatch <repatch42@yahoo.com>
wrote:
money wasted, (a penny wasted on each of a million units is $10,000 of
lost revenue!) and any designer worth his salt needs to learn how to
work without that expensive a net.
--
John Fields
wrote:
I disagree. Resistors not needed for a specific reason represent
money wasted, (a penny wasted on each of a million units is $10,000 of
lost revenue!) and any designer worth his salt needs to learn how to
work without that expensive a net.
--
John Fields